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Houseflies
DESCRIPTION
Order: Diptera (‘two-winged’)
Characteristics:
Single pair of membranous wings; hindwings modified as halteres; suctorial
mouthparts, piercing or non-piercing; large compound eyes; tarsi, 5-segmented;
metamorphosis complete with egg, larval, pupal and adult stages.
Family: Muscidae.
Insects with cylindrical bodies and a pronounced rostrum (snout) equipped
with mouthparts which is used by females as a boring tool; elbowed, clubbed
antennae set on rostrum; 4-segmented tarsi.
Species characteristics:
Common Housefly (Musca domestica)
Adults, 6-8mm long with 13-15mm wingspan; grey thorax with 4 longitudinal
dark stripes; basal half of abdomen buff-coloured and occasionally transparent
at sides, with central dark band broadening to cover last abdominal segments;
at rest, wings are spread; venation shows a sharp upward bend of 4th vein
at apical end.
Lesser Housefly (Fannia canicularis)
Adults, 6mm long with 12mm wingspan; grey thorax with 3 longitudinal stripes,
less pronounced than those of Common housefly; extensive yellow patch
at base of abdomen; at rest, wings are folded along back; venation shows
4th vein extending straight to wing margin.
DISTRIBUTION
Common houseflies (M. domestica) are ubiquitous insects, with a
flight range of at least kilometres (5 miles). They are highly active
indoors. In colder climates breeding generally ceases before winter, whereupon
the insects overwinter either as pupae or adults. However, in warm environments
houseflies remain active and reproduce throughout the year.
Lesser houseflies (F. canicularis) are frequently encountered in poultry
houses. They have an erratic flight pattern and are often seen flying
in large numbers around indoor light fittings. The Lesser housefly is
more tolerant of cool conditions than the Common housefly. This species
survives the winter mainly in the form of pupae, although, as with the
Common housefly, adults remain active and reproduce throughout the year
in warm conditions.
Houseflies can transmit intestinal worms, or their eggs, and are potential
vectors of diseases such as dysentery, gastroenteritis, typhoid, cholera
and tuberculosis. They will frequent and feed indiscriminately on any
liquefiable solid food, which may equally be moist, putrefying material
or food stored for human consumption.
Flies liquefy food by regurgitating digestive juices and their stomach
contents on to the food substance. This ‘liquid’ is then drawn up by the
suctorial mouthparts and in so doing the insects pick up pathogenic organisms,
which may collect on their bodies to be transferred on contact with other
surfaces or survive passage through the gut to be deposited as fly spots.
Fly spotting, produced when the insect feeds or defecates, results in
rejection of contaminated farm produce, for example eggs, at point of
sale. Furthermore, flies are frequently the subject of complaints to environmental
health authorities, causing major problems where infestations over-spill
from breeding sites such as rubbish tips and animal houses.
The Lesser housefly makes longer flights and spends less time resting
than the Common housefly. Females of the species tend to remain near the
breeding sites and only the males migrate. For these reasons F. canicularis
is less prone to transmit disease than M. domestica, but large
populations and similar feeding habits mean that this insect, too, has
a considerable potential to act as a vector of disease. It has occasionally
been implicated as a vector of intestinal or urinary myiasis.
LIFE-CYCLE
Common Housefly
Forty-eight hours after emergence as an adult, the female commences egg
laying. During her adult life of 1-3 months she is capable of producing
4-5 batches of 100-150 eggs. The pearly-white cylindrical eggs, 1mm in
length, are laid in moist decaying matter such as household refuse, compost
or dung. The eggs hatch in 8-48 hours, giving the smooth, white, legless
maggot larvae. These burrow away from light, seeking an optimal temperature
of 21-32°C, and after 3 moults reach maturity at a length of 10-12mm.
In the summer larval development may be completed within a few days, but
in winter this process may take more than a month. When mature, the larvae
leave the breeding site for the cooler surrounding areas; e.g. soil. Here
they develop as yellow, brown or black pupae 6mm long. Depending upon
conditions, adults emerge 3 days to 4 weeks later. The full cycle is generally
completed between one and 4 weeks, depending upon temperature.
It is clear that there is considerable potential for the development of
huge populations. Under temperate conditions as many as 12 generations
of flies may breed in one season whilst under tropical conditions even
this rate of reproduction will be exceeded.
Lesser Housefly
Lesser houseflies are prolific breeders in poultry manure, but will also
breed in other moist decaying matter. Egg laying commences when the female
is 10 days old. The eggs are banana-shaped, 1mm in length and bear a pair
of longitudinal ridges which assist flotation in a liquid medium. The
flattened, legless, grey-brown maggots hatch within 24-48 hours. Hairy
protuberances on their dorsal surface are thought to aid progression and
floating in a semi-liquid medium. The newly hatched larvae frequently
wander for a time before burrowing into a suitable food. Larval development
requires a minimum period of 8 days, during which time the larva passes
through 3 stages, eventually attaining a length of 6mm. Pupation requires
a drier location and lasts for at least 10 days. Development from egg
to adult emergence takes 3 weeks, although cooler conditions prolong this
period.
CONTROL
Flies have rapid, prolific breeding habits and high mobility. In order
to break the life-cycle, control measures should be directed against larval
and adult flies.
a) Hygiene/management
Satisfactory hygiene is necessary to limit potential breeding sites and
food sources.
Domestic refuse: this must be stored in well sealed bins, for early
removal to disposal sites. High-risk material should be sealed in bags
and burnt wherever possible. Refuse tips should be covered with earth,
to a depth of at least 230mm (9 inches), and then compacted. This will
minimize larval emergence and promote fermentation temperatures at which
larvae cannot survive.
Farm manure: manure should be kept as dry as possible, especially
in poultry houses, where leaking water feeders can provide ideal, moist
breeding conditions. The Biothermic method of storing dung involves compacting
manure into a cuboid stack, a method particularly suited to horse manure.
This form of storage promotes uniform, persistent fermentation throughout
the dung, which is lethal to larvae. Tarpaulins can also be used to cover
heaps, in order to prevent egg laying and conserve the heat of fermentation.
Entry of adult flies into buildings can be prevented by 1.18mm-mesh fly-screens
(which can easily be removed for cleaning), air curtains, bead screens
or self-closing doors equipped with rubber flaps.
b) Physical control using maggot traps
Maggot traps take advantage of the fact that larvae need to migrate from
breeding sites to cooler surroundings in order to pupate. A simple trap
consists of a concrete platform, on which manure or refuse is stored,
surrounded by a water-filled moat in which migrating larvae are trapped.
c) Insecticides
In order to obtain the best results, insecticidal control measures should
be integrated with good hygiene.
Glossary of terms
Halteres: Club-shaped balancing organs.
Suctorial: Capable of sucking.
Tarsus (Tarsi): Apical section of leg (the foot).
ADVICE
Valent BioSciences has an extensive range of products specifically formulated
for the control of flying and crawling insect pests.
Further information on all Valent BioSciences' household insecticide products
is available from:
Valent BioSciences Corporation
870 Technology Way
Suite 100
Libertyville, IL 60048
The greatest care has been taken to ensure the accuracy of the information
contained in this Fact Sheet. Under no circumstance, however, will Valent
BioSciences Corporation be liable in respect of any error or omission.
© Copyright Valent BioSciences Corporation 2001
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